Image display

ABSTRACT

In an image display device which includes an image display panel, in which two or more groups of particles having different colors and different charge characteristics are sealed in a plurality of cells formed by partition walls between two substrates, at least one of two substrates being transparent, and, in which the particles, to which an electrostatic field produced by electrodes provided to both of the substrates is applied, are made to move so as to display an image, as the electrodes provided on two substrates, use is made of a pattern electrode patternized in such a manner that a coating area of the electrode satisfies a predetermined condition with respect to a projected area of respective cells (first invention) or a pattern electrode patternized in such a manner that no electrode portion is formed at a vertically lower portion in respective cells (second invention).

TECHNICAL FIELD

The present invention relates to an image display device comprising animage display panel used for a reversible image display device enablesto repeatedly display images accompanied by flight and movement ofparticles utilizing Coulomb's force and so on and particularly relatesto an image display device in which even and excellent image can bedisplayed.

BACKGROUND ART

As an image display device substitutable for liquid crystal display(LCD), image display devices with the use of technology such as anelectrophoresis method, an electro-chromic method, a thermal method,dichroic-particles-rotary method are proposed.

As for these image display devices, it is conceivable as inexpensivevisual display device of the next generation from a merit having widefield of vision close to normal printed matter, having smallerconsumption with LCD, spreading out to a display for portable device,and an electronic paper is expected. Recently, electrophoresis method isproposed that microencapsulate dispersion liquid made up with dispersionparticles and coloration solution and dispose the liquid between facedsubstrates.

However, in the electrophoresis method, there is a problem that aresponse rate is slow by the reason of viscosity resistance because theparticles migrate among the electrophoresis solution. Further, there isa problem of lacking imaging repetition stability, because particleswith high specific gravity of titanium oxide is scattered withinsolution of low specific gravity, it is easy to subside, difficult tomaintain a stability of dispersion state. Even in the case ofmicroencapsulating, cell size is diminished to a microcapsule level inorder to make it hard to appear, however, an essential problem was notovercome at all.

Besides the electrophoresis method using behavior in the solution,recently, a method wherein electro-conductive particles and a chargetransport layer are installed in a part of the substrate without usingsolution is proposed. [The Imaging Society of Japan “Japan Hardcopy '99”(Jul. 21-23, 1999) Transaction Pages 249-252] However, the structurebecomes complicated because the charge transport layer and further acharge generation layer are to be arranged. In addition, it is difficultto constantly dissipate charges from the electro-conductive particles,and thus there is a drawback on the lack of stability.

In order to solve the problems mentioned above, it is known an imagedisplay device which comprises an image display panel, in which two ormore groups of particles having different colors and different chargecharacteristics are sealed in a plurality of cells formed by partitionwalls between two substrates, at least one of two substrates beingtransparent, and, in which the particles, to which an electrostaticfield produced by electrodes provided to both of the substrate isapplied, are made to fly and move so as to display an image by utilizingCoulomb's force.

In the image display device mentioned above, a plurality of cells areformed between two substrates in such a manner that: a transparentconductive material such as ITO and so on formed on a surface of a glasssubstrate is etched so as to form a patternized electrode such as a lineshape and so on; and partition walls are formed thereon by utilizing aphoto-resist.

In this case, since a coating area of the conductive material is made tobe 100% with respect to a projected area of respective cells, theparticles are unevenly distributed to a portion of the partition wallsformed around respective cells after driving a display cell. As aresult, the particles not only come short at a center portion ofrespective cells but also produce three groups of agglutination memberssuch as “positive charge—positive charge”, “positive charge—negativecharge” and “negative charge—negative charge” when the particles aregathered at the partition walls due to van der Waals force,electrostatic force and so on. Accordingly, there is a problem suchthat: “particle drop (phenomenon wherein a display due to a part of theparticles in the display element is missed)” is generated at the centerportion of respective cells; and thus an appearance becomes worse.

Moreover, since a coating area of the conductive material is made to be100% with respect to a projected area of respective cells, the particlesare moved downward of the cell due to a gravity and are gathered after along-term use in the case of arranging the image display panelvertically in a stationary manner. As a result, the particles not onlycome short at a center portion of respective cells but also produce anagglutination member at a lower portion of the cell. Accordingly, thereis a problem such that: “particle drop (phenomenon wherein a display dueto a part of the particles in the display element is missed)” isgenerated at the center portion of respective cells; and thus anappearance becomes worse.

DISCLOSURE OF INVENTION

The present invention is achieved to solve the problems mentioned aboveand has for its object to provide an image display device which candisplay even and excellent image due to a prevention of uneven particledistribution to the partition walls and a prevention of particle drop atthe center portion of respective cells, by using a pattern electrodewhich defines a coating area of the electrode with respect to aprojected area of respective cells, or, by using a pattern electrodehaving no electrode portion formed at a vertically lower portion inrespective cells.

In order to achieve the object mentioned above, according to a firstaspect of the invention, an image display device which comprises animage display panel, in which two or more groups of particles havingdifferent colors and different charge characteristics are sealed in aplurality of cells formed by partition walls between two substrates, atleast one of two substrates being transparent, and, in which theparticles, to which an electrostatic field produced by electrodesprovided to both of the substrates is applied, are made to move so as todisplay an image, is characterized in that a coating area of theelectrode provided on two substrates respectively is patternized withrespect to a projected area of respective cells.

In the image display device according to the first aspect of theinvention having the construction mentioned above, it is possible toprovide the image display device having rapid response rate due to a drytype display, simple construction, inexpensive cost and excellentstability, by constructing a new image display device in which imagedisplay elements enabling to move the particles, to which electrostaticfield is directly applied, are arranged in a matrix manner. Further,since a coating area of the electrode provided on two substratesrespectively is patternized with respect to a projected area ofrespective cells, the uneven particle distribution to the partitionwalls and the particle drop at the center portion of respective cellscan be prevented, and thus it is possible to provide the image displaydevice which can display even and excellent image.

In the image display device according to the first aspect of theinvention, in order to prevent the uneven particle distribution to thepartition walls and the particle drop at the center portion ofrespective cells, it is preferred that at least one of the electrodesprovided on the two substrates respectively has a coating area inrespective cells of 5-99% with respect to a projected area of respectivecells, or, that at least one of the electrodes provided on the twosubstrates respectively has a coating area in respective cells of 5-99%with respect to a projected area of respective cells.

Moreover, in the image display device according to the first aspect ofthe invention, in order to further prevent the uneven particledistribution to the partition walls and the particle drop at the centerportion of respective cells, it is preferred that a contact dimensionbetween at least one of the electrodes provided on the two substratesrespectively and the partition wall is less than 50% of an innerperipheral dimension-of respective cells.

Further, in order to achieve the object mentioned above, according to asecond aspect of the invention, an image display device which comprisesan image display panel, in which two or more groups of particles havingdifferent colors and different charge characteristics are sealed in aplurality of cells formed by partition walls between two substrates, atleast one of two substrates being transparent, and, in which theparticles, to which an electrostatic field produced by electrodesprovided to both of the substrates is applied, are made to move so as todisplay an image, is characterized in that, in the case of arranging theimage display panel vertically in a stationary manner, the electrode ispatternized in such a manner that no electrode portion is formed at avertically lower portion in respective cells.

In the image display device according to the second aspect of theinvention it is possible to provide the image display device havingrapid response rate due to a dry type display, simple construction,inexpensive cost and excellent stability, by constructing a new imagedisplay device in which image display elements enabling to move theparticles, to which electrostatic field is directly applied, arearranged in a matrix manner. Further, since in the case of arranging theimage display panel vertically in a stationary manner, the electrode ispatternized in such a manner that no electrode portion is formed at avertically lower portion in respective cells, the uneven particledistribution to the partition walls and the particle drop at the centerportion of respective cells can be prevented, and thus it is possible toprovide the image display device which can display even and excellentimage.

In the image display device according to the second aspect of theinvention, in order to prevent the uneven particle distribution to thepartition walls and the particle drop at the center portion ofrespective cells, it is preferred that an area of the no electrodeportion formed at a vertically lower portion in respective cells is5-50% with respect to a projected area of respective cells, or, that anarea of the no electrode portion formed at a vertically lower portion inrespective cells is 15-45% with respect to a projected area ofrespective cells.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 a-1 c are schematic-views respectively explaining one embodimentof a display element of an image display panel utilized in an imagedisplay device according to the invention, and its display operationtheory.

FIGS. 2 a and 2 b are schematic views respectively explaining the imagedisplay panel of the image display device according to the invention.

FIG. 3 is a schematic view showing a shape of a display cell formed bypartition walls.

FIG. 4 is a schematic view illustrating a method for measuring a surfacepotential of particles utilized in the image display device according tothe invention.

FIGS. 5 a-5 c are schematic views respectively depicting a patternelectrode with the partition wall in examples 1-3 according to a firstaspect of the invention.

FIGS. 6 a-6 c are schematic views respectively showing the patternelectrode with the partition wall in comparative examples 1-3 accordingto the first aspect of the invention.

FIGS. 7 a-7 c are schematic views respectively illustrating the patternelectrode with the partition wall in examples 11-13 according to asecond aspect of the invention.

FIGS. 8 a and 8 b are schematic views respectively depicting the patternelectrode with the partition wall in comparative examples 11, 12according to the second aspect of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the embodiments according to the invention will beexplained in detail with reference to the drawings. FIGS. 1 a to 1 c areschematic views respectively showing one embodiment of the image displayelement of the image display panel used for the image display deviceaccording to the invention, and its operation theory. In the embodimentsshown in FIGS. 1 a to 1 c, numeral 1 is a transparent substrate, numeral2 is an opposed substrate, numeral 3 is a display electrode (transparentelectrode), numeral 4 is an opposed electrode, numeral 5 is a negativelychargeable particle, numeral 6 is a positively chargeable particle andnumeral 7 is a partition wall.

FIG. 1 a shows a state such that the negatively chargeable particles 5and the positively chargeable particles 6 are arranged between opposedsubstrates (transparent substrate 1 and opposed substrate 2). Under sucha state, when a voltage is applied in such a manner that a side of thedisplay electrode 3 becomes low potential and a side of the opposedelectrode 4 becomes high potential, as shown in FIG. 1 b, the positivelychargeable particles 6 fly and move to the side of the display electrode3 and the negatively chargeable particles 5 fly and move to the side ofthe opposed electrode 4 by means of Coulomb's force. In this case, adisplay face viewed from a side of the transparent substrate 1 lookslike a color of the positively chargeable particles 6. Next, when avoltage is applied in such a manner that the side of the displayelectrode 3 becomes high potential and the side of the opposed electrode4 becomes low potential by reversing potentials, as shown in FIG. 1 c,the negatively chargeable particles 5 fly and move to the side of thedisplay electrode 3 and the positively chargeable particles 6 fly andmove to the side of the opposed electrode 4 by means of Coulomb's force.In this case, the display face viewed from the side of the transparentsubstrate 1 looks like a color of the negatively chargeable particles 5.

The display states shown in FIGS. 1 b and 1 c are repeatedly changeableonly by reversing the potentials of a power source, and thus it ispossible to change colors on the display face reversibly by reversingthe potentials of the power source as mentioned above. The colors of theparticles can be arbitrarily selected. For example, when the negativelychargeable particles 5 are white color and the positively chargeableparticles 6 are black color, or, when the negatively chargeableparticles 5 are black color and the positively chargeable particles 5are white color, a reversible image display between white color andblack color can be performed. In this method, since the particles areonce adhered to the electrode by means of an imaging force, a displayimage can be maintained for a long time after a voltage apply isstopped, thereby showing an excellent memory property.

In the first aspect of the invention, since the chargeable particles flyand move in the gas, the response speed of the image display isextremely fast and the response speed of shorter than 1 msec may bepossible. Moreover, it is not necessary to use an orientation film and apolarizing plate as the liquid crystal display, and thus it is possibleto make the structure simple and to realize the image display devicehaving a large display area at a lower cost. In addition, it is stablewith respect to a temperature variation and can be used in a widetemperature range from a low temperature to a high temperature. Further,it is not affected by an angle of visual field and has a high reflectioncoefficient. Therefore, it is easily viewable and has low electric powerconsumption. Furthermore, it has an excellent memory property and thusit is not necessary to use an electric power when the image is to bemaintained.

The image display device according to the invention comprises the imagedisplay panel in which the image display element mentioned above isarranged in a matrix manner. FIGS. 2 a and 2 b show such one embodimentrespectively. In this embodiment, 3×3 matrix is shown for convenience ofexplanation. When the number of the electrodes is n, it is possible toconstruct an arbitrary n×n matrix.

In the embodiment shown in FIGS. 2 a and 2 b, display electrodes 3-1 to3-3 arranged substantially in parallel with each other and opposedelectrodes 4-1 to 4-3 arranged substantially in parallel with each otherare provided respectively on the transparent substrate 1 and the opposedsubstrate 2 in such a manner that they are intersected with each other.Serial switches SW3-1-1, SW3-2-1; and SW3-3-1 are respectively connectedto the display electrodes 3-1 to 3-3. In the same way, serial switchesSW4-1-1, SW4-2-1 and SW4-3-1 are respectively connected to the opposedelectrodes 4-1 to 4-3. Further, serial switch SW3-1-2 is connected toSW3-1-1, SW3-2-1 and SW3-3-1 in common, and serial switch SW4-1-2 isconnected to SW4-1-1, SW4-2-1 and SW4-3-1 in common.

The switches SW3-n-1 (n=1-3) and the switches SW4-n-1 (n=1-3) serve toswitch the connection toward a ground level and the connection towardthe next SW3-1-2, respectively. The switches SW3-1-2 and the switchesSW4-1-2 serve to switch the connection toward a high voltage generatingcircuit 8 and the connection toward a low voltage generating circuit 9respectively. The all the serial switches SW constitute a matrix drivecircuit 10. In this embodiment, the 3×3 image display elements areconstructed by isolating them by means of the partitions 7.

The operation of the matrix electrode constructed by the displayelectrodes 3-1 to 3-3 and the opposed electrodes 4-1 to 4-3 mentionedabove is performed in such a manner that, in accordance with the imageto be displayed, open/close operations of respective switches SW arecontrolled by means of a sequencer not shown and the 3×3 image displayelements are displayed in sequence. This operation is the same as thatof the known one basically.

With respect to respective electrodes constituting the matrix electrode,in the case that use is made of the display electrode on the transparentsubstrate, the display electrode is formed of electroconductivematerials, which are transparent and have pattern formation capability.As such electroconductive materials, metals such as aluminum, silver,nickel, copper and gold, or transparent electroconductive metal oxidessuch as ITO, electroconductive tin oxide and electroconductive zincoxide formed in the shape of thin film by sputtering method, vacuumvapor deposition method, CVD method, and coating method, or coatedmaterials obtained by applying the mixed solution of anelectroconductive agent with a solvent or a synthetic resin binder areused.

Typical examples of the electroconductive materials include cationicpolyelectrolyte such as benzyltrimethylammonium chloride,tetrabutylammonium perchlorate and so on, anionic polyelectrolyte suchas polystyrenesulfonate, polyacrylate, and so on, or electroconductivefine powders of zinc oxide, tin oxide, or indium oxide. Additionally,the thickness of the electrode may be suitable unless theelectroconductivity is absent or any hindrance exists in opticaltransparency, and it is preferable to be 3 to 1000 nm, more preferableto be 5 to 400 nm. The foregoing transparent electrode materials can beemployed as the electrode arranged on the opposed substrate. However,non-transparent electrode materials such as aluminum, silver, nickel,copper, and gold can be also employed if it is not necessary to use thetransparent electrode.

It is preferred that an insulation coating layer is formed on theelectrode so as not to reduce charges of the charged particles. As suchinsulation coating layer, if use is made of a positively chargeableresin with respect to the negatively chargeable particles and anegatively chargeable resin with respect to the positively chargeableparticles, the charges of the particles are to be difficult to reduceand it is particularly preferable.

Hereinafter, the substrate used in the image display device according tothe invention will be explained. With respect to the substrate, at leastone of the substrates is the transparent substrate through which a colorof the particles can be observed from outside of the device, and it ispreferred to use a material having a high transmission factor of visiblelight and an excellent heat resistance. Whether a flexibility of thesubstrate is necessary or not is suitably selected in accordance withits use. For example, it is preferred to use a material havingflexibility for the use of electronic paper and so on, and it ispreferred to use a material having no flexibility for the use of adisplay of portable device such as mobile phone, PDA, laptop computerand so on.

Examples of the substrate material include polymer sheets such aspolyethylene terephthalate, polyether sulfone, polyethylene,polycarbonate, polyimide or acryl and inorganic sheets such as glass,quartz or so. The opposed substrate may be transparent or may be opaque.The thickness of the substrate is preferably 2 to 5000 μm, morepreferably 5 to 1000 μm. When the thickness is too thin, it becomesdifficult to maintain strength and distance uniformity between thesubstrates, and when the thickness is too thick, vividness and contrastas a display capability degrade, and in particular, flexibility in thecase of using for an electronic paper deteriorates.

Moreover, as shown in FIG. 2 a, it is preferred to arrange the partitionwall 7 to respective display elements. The display cell formed by thepartition walls each made of rib has a square shape, a triangular shape,a line shape, a circular shape, a hexagon shape as shown in FIG. 3viewed from a plane surface of the substrate, and the arrangementthereof is grid-like, honeycomb and so on.

In this manner, it is possible to prevent an unnecessary movement of theparticles in a direction parallel to the substrate, to help a repeatedlyendurance property and a memory maintaining property and to improve astrength of the image display panel by making a distance between thesubstrates even and strong. The formation method of the partition wallis not particularly restricted, however, a screen printing methodwherein pastes are overlapped by coating repeatedly on a predeterminedposition by screen plate; a sandblast method wherein partition materialsare painted with a desired thickness entirely over the substrate andthen after coating resist pattern on the partition materials which iswanted to be left as a partition, jetting abrasive to cut and removepartition materials aside from the partition part; lift-off method(additive method) wherein a resist pattern is formed on the substrateusing photosensitive polymer, and then after burying paste into a resistrecess, removing the resist; photolithography method wherein thephotosensitive resin composition containing the partition materials isapplied over the substrate and then obtaining a desired pattern byexposure & developing; and mold formation method wherein pastecontaining the partition materials is applied over the substrate andthen forming a partition by compression bonding & pressure forming thedies having rugged structure; and so on are adopted. Further, modifyingthe mold formation method, relief embossing method wherein a reliefpattern provided by a photosensitive polymer composition is used as amold is also adopted. Among them, the photolithography method using theresist film is preferably used. Furthermore, it is preferred to set awidth of the partition wall to 1-100 μm more preferably 5-100 μm

Hereinafter, the particles used in the image display device according tothe invention will be explained. In the present invention, as theparticles for display, although any of colored particles negatively orpositively chargeable having capability of flying and moving byCoulomb's force are employable, spherical particles with light specificgravity are particularly preferable. The average particle diameter ofthe particles is preferable to be 0.1 to 50 μm, particularly to be 1 to30 μm. When the particle diameter is less than this range, chargedensity of the particles will be so large that an imaging force to anelectrode and a substrate becomes too strong; resulting in poorfollowing ability at the inversion of its electric field, although thememory characteristic is favorable. On the contrary, when the particlediameter exceeds the range, the following ability is favorable, but thememory characteristic will degrade.

Although the method for charging the particles negatively or positivelyis not particularly limited, a corona discharge method, an electrodeinjection-charge method, a friction charge method and so on areemployable. It is preferred that the particle measured by a blow-offmethod by using carriers has a surface charge density not less than 5μm/m² and not greater than 150 μm/m². When the absolute value of thesurface charge density of the particles is smaller than this range, theresponse speed in response to a deviation of the electrostatic fieldbecomes slower and the memory characteristics become lower. When theabsolute value of the surface charge density of the particles is largerthan this range, an imaging force to the substrate and electrode becomestoo stronger. Therefore, the following ability at the inversion of itselectric field becomes poor, but the memory characteristic is favorable.

A charge amount measurement and a particle gravity measurement, whichare necessary to calculate the surface charge density used in theinvention, can be performed as mentioned below. That is, according to ablow-off method, the particles and carrier particles are sufficientlycontacted and a saturated charge amount thereof is measured, so that acharge amount per a unit weight of the particles can be measured. Then,a particle diameter and a specific gravity of the particles areseparately measured, and the surface charge density of the particles iscalculated by using them.

<Blow-Off Measuring Theory and Method>

In the blow-off method, a mixture of the powders and the carriers areplaced into a cylindrical container with nets at both ends, andhigh-pressure gas is blown from the one end to separate the powders andthe carriers, and then only the powders are blown off from the mesh ofthe net. In this occasion, charge amount of reverse blown polarityremains on the carriers with the same charge amount of the powderscarried away out of the container. Then, all of electric flux by thiselectric charge are collected to Faraday cage, and are charged across acapacitor with this amount. Accordingly, the charge amount of theparticles is determined as Q=CV (C: capacity, V: voltage across bothends of the capacitor) by measuring potential of both ends of thecapacitor.

In the invention, as a blow-off powder charge amount measuringinstrument, TB-200 produced by Toshiba Chemical Co., Ltd. was used,F963-2535 available from Powder TEC Co., Ltd. was employed as the samekind of carriers, and a specific gravity of the particle substanceconstituting the particles was measured by a multi-volume density meterH1305 produced by Shimadzu Corporation. Then, the charge density perunit surface area (unit: μC/m²) was calculated.

Because it is necessary for the particles to hold the charged electriccharge, insulating particles with the volume specific resistance of1×10¹⁰ Ω·cm or greater are preferable, and in particular,-insulatingparticles with the volume specific resistance of 1×10¹² Ω·cm or greaterare more preferable. Further, the particles with slow charge attenuationproperty evaluated by the measuring method below are more preferable.

That is, the particles are made into a film having a thickness of 5-100μm by means of a press method, a heating/melting method, a castingmethod and so on, and the voltage of 8 kV is applied to a Coronagenerator disposed with a distance of 1 mm to the film surface so as togenerate Corona discharge, which charges the film surface. Then, thechange of the surface potential is measured to determine thesuitability. In this occasion, it is preferable to select the materialwhose maximum surface potential will be 300 V or greater after 0.3seconds, more preferable to select the material whose maximum surfacepotential will be 400 V or greater after 0.3 second as the material forcomposing the particles.

Additionally, the foregoing surface potential is measured by means of aninstrument (CRT2000 produced by QEA Inc.) as shown in FIG. 4. In thisinstrument both end portions of a roll shaft being held with chuck 31,compact scorotron discharger 32 and surface potential meter 33 arespaced with predetermined interval to form a measurement unit. Facedlydeploying the measurement unit with a distance of 1 mm from the surfaceof the film, and by moving the measurement unit from one end portion ofthe roll shaft to the other end portion with an uniform speed, with thestate that the roll shaft remains stopping and while giving surfacecharge, a method of measuring its surface potential is preferablyadopted. Moreover, measurement environment should be settled at thetemperature of 25±3° C. and the humidity of 55±5% RH.

If the particles satisfy electrostatic property and so on, the particlesmay be formed by any materials. For example, it is formed by resin,charge control agent, coloring agent, inorganic additive and so on, or,by coloring agent and so on only.

Typical examples of the resin include urethane resin, urea resin,acrylic resin, polyester resin, acryl urethane resin, acryl urethanesilicone resin, acryl urethane fluorocarbon polymers, acryl fluorocarbonpolymers, silicone resin, acryl silicone resin, epoxy resin, polystyreneresin, styrene acrylic resin, polyolefin resin, butyral resin,vinylidene chloride resin, melamine resin, phenolic resin, fluorocarbonpolymers, polycarbonate resin, polysulfon resin, polyether resin, andpolyamide resin. For the purpose of controlling the attaching force withthe substrate, acryl urethane resin, acryl silicone resin, acrylfluorocarbon polymers, acryl urethane silicone resin, acryl urethanefluorocarbon polymers, fluorocarbon polymers, silicone resin areparticularly preferable. Two kinds or more of these may be mixed andused.

Examples of the electric charge control agent include, but notparticularly specified to, negative charge control agent such assalicylic acid metal complex, metal containing azo dye, oil-soluble dyeof metal-containing (containing a metal ion or a metal atom), the fourthgrade ammonium salt-based compound, calixarene compound,boron-containing compound (benzyl acid boron complex), andnitroimidazole derivative. Examples of the positive charge control agentinclude nigrosine dye, triphenylmethane compound, the fourth gradeammonium salt compound, polyamine resin, imidazole derivatives, etc.Additionally, metal oxides such as ultra-fine particles of silica,ultra-fine particles of titanium oxide, ultra-fine particles of alumina,and so on; nitrogen-containing circular compound such as pyridine, andso on, and these derivates or salts; and resins containing variousorganic pigments, fluorine, chlorine, nitrogen, etc. can be employed asthe electric charge control agent.

As for a coloring agent, various kinds of organic or inorganic pigmentsor dye as will be described below are employable.

Examples of black pigments include carbon black, copper oxide, manganesedioxide, aniline black, and activate carbon. Examples of yellow pigmentsinclude chrome yellow, zinc chromate, cadmium yellow, yellow iron oxide,mineral first yellow, nickel titanium yellow, navel orange yellow,naphthol yellow S, hanzayellow G, hanzayellow 10G, benzidine yellow G,benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, andtartrazinelake. Examples of orange pigments include red chrome yellow,molybdenum orange, permanent orange GTR, pyrazolone orange, Balkanorange, Indanthrene brilliant orange RK, benzidine orange G, andIndanthrene brilliant orange GK. Examples of red pigments include redoxide, cadmium red, diachylon, mercury sulfide, cadmium, permanent red4R, lithol red, pyrazolone red, watching red, calcium salt, lake red D,brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, andbrilliant carmine 3B.

Examples of purple pigments include manganese purple, first violet B,and methyl violet lake. Examples of blue pigments include Berlin blue,cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue,metal-free phthalocyanine blue, partially chlorinated phthalocyanineblue, first sky blue, and Indanthrene blue BC. Examples of greenpigments include chrome green, chromium oxide, pigment green B,Malachite green lake, and final yellow green G. Further, examples ofwhite pigments include zinc white, titanium oxide, antimony white, andzinc sulphide.

Examples of extenders include baryta powder, barium carbonate, clay,silica, white carbon, talc, and alumina white. Furthermore, there areNigrosine, Methylene Blue, rose bengal, quinoline yellow, andultramarine blue as various dyes such as basic dye, acidic dye,dispersion dye, direct dye, etc. These coloring agents may be used aloneor in combination of two or more kinds thereof. Particularly, carbonblack is preferable as the black coloring agent, and titanium oxide ispreferable as the white coloring agent.

Although the manufacturing method of the particles is not specificallyrestricted, mixing/grinding method or polymerization method forproducing toner of electrophotography is, for example, similarlyemployable. Further the method of coating resin or charge control agentand so on over the surface of powders such as inorganic or organicpigments is also employable.

The distance between the transparent substrate and the opposed substrateis suitably adjusted in a manner where the particles can move andmaintain the contrast of image display; however, it is adjusted usuallywithin 10 to 5000 μm, preferably within 30 to 500 μm. Moreover, theparticle filling amount (volume occupying rate) of the particlesexisting in the space between the faced substrates is preferable to be 5to 70 vol %, more preferable to be 10 to 65 vol %, further morepreferable to be 10 to 55 vol %. When the volume occupying rate of theparticles is less than 5 vol %, it is not possible to display a clearimage. When the volume occupying rate of the particles exceeds 70 vol %,the particles are not easily moved. Here, the volume of space means avolume, in which the particles can be filled, obtained by substitutingan occupied portion of the partition wall 4 and a seal portion of thedevice from a portion sandwiched between the opposed substrates 1 and 2.

Further, in the present invention, it is important to control a gas in agap surrounding particles between the substrates, and a suitable gascontrol contributes an improvement of a display stability. Specifically,it is important to control a humidity of the gap gas to not more than60% RH at 25° C., preferably not more than 50% RH, more preferably notmore than 35% RH.

In the image display panel used in the image display device according tothe invention, plural of the foregoing display elements are disposed ina matrix form, and images can be displayed. In the case of monochromedisplay, one display element makes one pixel. In the case of full colordisplay, three kinds of display elements, i.e., one group of displayelements each having color plate of R (red), G (green) and B (blue)respectively and each having particles of black composes a set ofdisposed elements preferably resulting in the reversible image displaypanel having the sets of the elements.

A kind of the gap gas is not limited if it has the humidity mentionedabove, but it is preferred to use dry air, dry nitrogen gas, dry heliumgas, dry carbon dioxide gas, dry methane gas and so on.

It is necessary to seal this gas in the device so as to maintain thehumidity mentioned above. For example, it is important to perform theoperations of filling the particles and assembling the substrate underan atmosphere having a predetermined humidity and to apply a seal memberand a seal method for preventing a humidity inclusion from outside ofthe device.

The image display device according to the invention is applicable to theimage display unit for mobile equipment such as notebook personalcomputers, PDAs, cellular phones and so on; to the electric paper forelectric book, electric newspaper and so on; to the bulletin boards suchas signboards, posters, blackboards and so on; to the image display unitfor electric calculator, home electric application products, autosupplies and so on; to the card display unit for point card, IC card andso on; and to the display unit for electric POP, electric advertisement,electric price tag, electric musical score, RF-ID device and so on.

Then, various examples of the pattern electrode in the image displaydevice according to the invention will be explained.

Examples According to a First Aspect of the Invention

In the image display device according to the first aspect of theinvention, a pattern electrode 12 shown in FIGS. 5 a, 5 b and 5 c(pattern electrodes 12-1-12-3) is used.

The pattern electrode 12 (the pattern electrodes 12-1-12-3) according tothe invention is patternized to have a predetermined pattern withrespect to respective cells 11 formed by a frame-like partition wall 7,and is used as the display electrode 3 and the opposed substrate 4.

The pattern electrode 12-1 shown in FIG. 5 a (hereinafter, referred aselectrode 1) is constructed only by a linear portion 12-1 a in such amanner that line spaces are formed at left and right ends in the cell11.

The pattern electrode 12-2 shown in FIG. 5 b (hereinafter, referred aselectrode 2) is constructed by a linear portion 12-2 a and a squareportion 12-2 b in such a manner that line spaces are formed at upper,lower, left and right ends in the cell 11.

The pattern electrode 12-2 shown in FIG. 5 c (hereinafter, referred aselectrode 3) is constructed by a linear portion 12-3 a and a circularportion 12-3 b in such a manner that spaces are formed at upper, lower,left and right peripheral portions in the cell 11.

Pattern electrodes 13 (13-1-13-3) shown in FIGS. 6 a, 6 b and 6 c arecomparative examples so as to be compared with the above examples of thepattern electrodes in the image display device according to theinvention.

The pattern electrode 13-1 shown in FIG. 6 a (hereinafter, referred aselectrode 4) is constructed only by a linear portion 13-1 a, whichcovers overall portion in the cell 11.

The pattern electrode 13-2 shown in FIG. 6 b (hereinafter, referred aselectrode 5) is constructed only by a narrow linear portion 13-2 a,which covers only a center portion in upper and lower directions in thecell 11.

The pattern electrode 13-3 shown in FIG. 6 c (hereinafter, referred aselectrode 6) is constructed by a linear portion 13-3 a and a hollowportion 13-3 b in such a manner that a square space is formed at acenter portion in the cell 11.

The image display devices including the electrode 1-electrode 6 weremanufactured as follows.

<Manufacture of Electrode Pattern>

The electrode 1-electrode 6 were obtained in such a manner that a dryphoto-resist was adhered to a glass substrate, to which indium oxidehaving thickness of about 500 A was arranged, and an exposing step, adeveloping step and an etching step were performed through a positivemask having respective electrode patterns.

<Manufacture of Partition Wall>

The pattern electrodes (electrode 1-electrode 6) with the partition wallshown in FIGS. 5 a-5 c and FIGS. 6 a-6 c were obtained in such a mannerthat a dry photo-resist having a thickness of 50 μm was adhered torespective electrodes manufactured as mentioned above, and an exposingstep and a developing step were performed through a negative mask havinga partition wall pattern of 50 μm partition wall and 50 μm □ cell.

<Manufacture of Particles>

Two kinds of the particles (particles A, particles B) were prepared.

The particles A (black color particles) were manufactured in such amanner that acrylic urethane resin: EAU53B (Asia Industry Co.,Ltd.)/IPDI cross-linking agent: Excel-Hardener HX (Asia Industry Co.,Ltd.), CB (Carbon Black) 4 phr, charge control agent: BontronN07 (OrientChemical Industries Ltd.) 2 phr were added, mixed, ground and classifiedby a jet-mill.

The particles B (white color particles) were manufactured in such amanner that acrylic urethane resin: EAU53B (Asia Industry Co.,Ltd.)/IPDI cross-linking agent: Excel-Hardener HX (Asia Industry Co.,Ltd.), titanium oxide 10 phr, charge control agent: BontronE89 (AsiaIndustry Co., Ltd.) 2 phr were added, mixed, ground and classified bythe jet-mill.

After that, the particles A and the particles B were filled to the thusprepared substrate, on which the pattern electrodes with the partitionwall were arranged, by 12 g/m² respectively with respect to theprojected area of the cell 11. Then, the same kind of the substrate, onwhich the pattern electrodes with the partition wall were arranged, wasstacked and connected as the opposed substrate to the substratementioned above by using epoxy adhesive, so that the image displaydevice in which a distance between the opposed substrates was 100 μm.

<Estimation of Display Function>

A voltage of 200 V was applied between the electrodes of the thusmanufactured image display device, and performances after inversion at50 times (initial state) and after inversion at 10000 times (enduredstate) were measured.

As the estimation method of the display function, a reflectance of whitedisplay and a reflectance of black display were measured at a centerportion of the cell by means of EYE SCALE 3 (Eye-Systems Incorporated),and then it was assumed as NG that a contrast of the initial state orthe endured state was not greater than 3. Here, a contrast ratio wascalculated from contrast ratio=(reflectance density of blackdisplay)/(reflectance density of white display).

If summarized the above, specifications of the electrode 1-electrode 6were summarized as the following Table 1, and estimations of theelectrode 1-electrode 6 were summarized as the following TABLE 1Electrode 1 Electrode 2 Electrode 3 Electrode 4 Electrode 5 Electrode 6Width of partition wall μm 50 50 50 50 50 50 Height of partition wall μm50 50 50 50 50 50 Area of display mm² 0.25 0.25 0.25 0.25 0.25 0.25portion (1) Inner circumference μm 2000 2000 2000 2000 2000 2000 ofdisplay portion (2) Electrode area in mm² 0.20 0.20 0.13 0.25 0.01 0.13display portion (3) Contact portion μm 800 100 100 2000 20 2000 betweenelectrode and partition wall (4) (3)/(1) % 80 80 52 100 4 52 (4)/(2) %40 5 5 100 1 100

TABLE 2 Comparative Comparative Comparative Example 1 Example 2 Example3 Example 1 Example 2 Example 3 Electrode μm electrode 1 electrode 2electrode 3 electrode 4 electrode 5 electrode 6 category (1) Electrodeμm electrode 1 electrode 2 electrode 3 electrode 4 electrode 5 electrode6 category (2) After reference 29.8 33.0 28.0 31.9 21.3 29.0 inversionof white at 50 times display % reference 4.2 4.4 4.3 4.2 14.2 16.1 ofblack display % contrast 7.1 7.5 6.5 7.6 1.5 1.8 After reference 28.630.8 28.1 14.0 17.3 25.9 inversion at of white 10000 times display %reference 4.4 4.6 4.6 5.2 14.4 16.2 of black display % contrast 6.5 6.76.1 2.7 1.2 1.6 Decision ◯ ◯ ◯ X X X

From the results shown in Table 1 and Table 2, the electrode 1-electrode3 of the examples 1-3, in which a coating area of the electrode inrespective cells was 80%, 80%, 52% with respect to the projected area ofrespective cells, and, in which a contact dimension between theelectrode and the partition wall was 40%, 5%, 5%, were estimated as OK.However, the electrode 4-electrode 6 of the comparative examples 1-3, inwhich a coating area of the electrode in respective cells was 100%, 4%,2% with respect to the projected area of respective cells, and, in whicha contact dimension between the electrode and.the partition wall was100%, 1%, 100%, were estimated as NG. Therefore, the followings wereunderstood.

-   (1) It is preferred that at least one of the electrodes provided to    the two substrates respectively has a coating area of the electrode    in respective cells such that it is 5-99% with respect to the    projected area of respective cells.-   (2) It is further preferred that at least one of the electrodes    provided to the two substrates respectively has a coating area of    the electrode in respective cells such that it is 30-90% with    respect to the projected area of respective cells.-   (3) It is preferred that a contact dimension between at least one of    the electrodes provided to the two substrates respectively and the    partition wall is less than 50% of an inner peripheral dimension of    respective cells.

Therefore, it is possible to obtain the image display panel having evenand excellent display function from the examples 1-3 corresponding tothe electrode 1-electrode 3, which satisfy all the conditions (1)-(3)mentioned above.

In the embodiment mentioned above, the electrodes (display electrode andopposed electrode are arranged to the substrates (transparent substrateand opposed substrate). In this case, a term “arranged to the substrate”means not only the case such that “the electrode is directly arranged onthe substrate” but also the case such that “the electrode is separatelyarranged on the substrate”.

Examples According to a Second Aspect of the Invention

In the image display device according to the second aspect of theinvention, a pattern electrode 22 shown in FIGS. 7 a, 7 b and 7 c(pattern electrodes 22-1-22-3) is used.

The pattern electrode 22 (the pattern electrodes 22-1-22-3) according tothe invention is patternized to have a predetermined pattern withrespect to respective cells 11 formed by a frame-like partition wall 7,and is used as the display electrode 3 and the opposed substrate 4.

The pattern electrode 22-1 shown in FIG. 7 a (hereinafter, referred aselectrode 11) is constructed by a linear portion 22-1 a and a squareportion 22-1 b in such a manner that a space extending in a horizontaldirection is formed at a vertically lower portion in respective cells 11in the case of arranging the image display panel vertically in astationary manner.

The pattern electrode 22-2 shown in FIG. 7 b (hereinafter, referred aselectrode 12) is constructed by a linear portion 22-2 a having a widthequal to that of the linear portion 22-1 a mentioned above and a squareportion 22-2 b having an area smaller than that of the square portion22-1 b mentioned above in such a manner that a space extending in ahorizontal direction is formed at a vertically lower portion inrespective cells 11 in the case of arranging the image display panelvertically in a stationary manner.

The pattern electrode 22-3 shown in FIG. 7 c (hereinafter, referred aselectrode 13) is constructed by a linear portion 22-3 a having a widthlarger than that of the linear portion 22-2 a mentioned above and asquare portion 22-3 b having an area equal to that of the square portion22-2 b mentioned above in such a manner that a space extending in ahorizontal direction is formed at a vertically lower portion inrespective cells 11 in the case of arranging the image display panelvertically in a stationary manner.

Pattern electrodes 23 (23-1, 23-2) shown in FIGS. 8 a and 8 b arecomparative examples so as to be compared with the above examples of thepattern electrodes in the image display device according to theinvention.

The pattern electrode 23-1 shown in FIG. 8 a (hereinafter, referred aselectrode 14) is constructed only by a linear portion 23-1 a, whichcovers overall portion in the cell 11 in the case of arranging the imagedisplay panel vertically in a stationary manner.

The pattern electrode 23-2 shown in FIG. 8 b (hereinafter, referred aselectrode 15) is constructed by a linear portion 23-2 a and a squareportion 23-2 b in such a manner that a space extending in a horizontaldirection is formed at a vertically lower portion in respective cells 11in the case of arranging the image display panel vertically in astationary manner. This electrode 15 inverts the electrode 12 up anddown vertically.

The image display devices including the electrode 11-electrode 15 weremanufactured as follows.

<Manufacture of Electrode Pattern>

The electrode 1-electrode 6 were obtained in such a manner that a dryphoto-resist was adhered to a glass substrate, to which indium oxidehaving thickness of about 500 Å was arranged, and an exposing step, adeveloping step and an etching step were performed through a positivemask having respective electrode patterns.

<Manufacture of Partition Wall>

The pattern electrodes (electrode 11-electrode 15) with the partitionwall shown in FIGS. 7 a-7 c and FIGS. 8 a and 8 b were obtained in sucha manner that a dry photo-resist having a thickness of 50 μm was adheredto respective electrodes manufactured as mentioned above, and anexposing step and a developing step were performed through a negativemask having a partition wall pattern of 50 μm partition wall and 50 μm □cell.

<Manufacture of Particles>

Two kinds of the particles (particles A, particles B) were prepared.

The particles A (black color particles) were manufactured in such amanner that acrylic urethane resin: EAU53B (Asia Industry Co.,Ltd.)/IPDI cross-linking agent: Excel-Hardener HX (Asia Industry Co.,Ltd.), CB (Carbon Black) 4 phr, charge control agent: BontronN07 (OrientChemical Industries Ltd.) 2 phr were added, mixed, ground and classifiedby a jet-mill.

The particles B (white color particles) were manufactured in such amanner that acrylic urethane resin: EAU53B (Asia Industry Co.,Ltd.)/IPDI cross-linking agent: Excel-Hardener HX (Asia Industry Co.,Ltd.), titanium oxide 10 phr, charge control agent: BontronE89 (AsiaIndustry Co., Ltd.) 2 phr were added, mixed, ground and classified bythe jet-mill.

After that, the particles A and the particles B were filled to the thusprepared substrate, on which the pattern electrodes with the partitionwall were arranged, by 12 g/m² respectively with respect to theprojected area of the cell 11. Then, the same kind of the substrate, onwhich the pattern electrodes with the partition wall were arranged, wasstacked and connected as the opposed substrate to the substratementioned above by using epoxy adhesive, so that the image displaydevice in which a distance between the opposed substrates was 100 μm.

<Estimation of Display Function>

A voltage of 200 V was applied between the electrodes of the thusmanufactured image display device, and performances after inversion at50 times (initial state) and after inversion at 10000 times (enduredstate) were measured.

As the estimation method of the display function, a reflectance of whitedisplay and a reflectance of black display were measured at a centerportion of the cell by means of EYE SCALE 3 (Eye-Systems Incorporated),and then it was assumed as NG that a contrast of the initial state orthe endured state was not greater than 3. Here, a contrast ratio wascalculated from contrast ratio=(reflectance density of blackdisplay)/(reflectance density of white display).

If summarized the above, specifications of the electrode 11-electrode 15were summarized as the following Table 3, and estimations of theelectrode 11-electrode 15 were summarized as the following Table 4.TABLE 3 Electrode Electrode Electrode Electrode Electrode 11 12 13 14 15Width of partition μm 50 50 50 50 50 wall Height of partition μm 50 5050 50 50 wall Area of display mm² 0.250 0.250 0.250 0.250 0.250 portion(1) Electrode area in mm² 0.205 0.151 0.190 0.250 0.151 display portionArea of no electrode mm² 0.045 0.099 0.060 0 0.099 portion in displayportion (2) (2)/(1) % 18 40 24 0 40 Region of arranging lower lowerlower — upper no electrode portion

TABLE 4 Comparative Comparative Example Example Example Example Example11 12 13 11 12 Electrode μm electrode electrode electrode electrodeelectrode category (1) 11 12 13 14 15 Electrode μm electrode electrodeelectrode electrode electrode category (2) 11 12 13 14 15 Afterinversion reference 32.3 30.2 29.0 31.9 31.8 at 50 times of whitedisplay % reference 4.3 4.2 4.2 4.2 4.3 of black display % contrast 7.57.2 6.9 7.6 7.4 After inversion reference 2.87 29.3 27.3 14.0 11.1 at10000 times of white display % reference 4.7 4.5 4.4 5.2 2.1 of blackdisplay % contrast 6.1 6.5 6.2 2.7 2.1 Decision ◯ ◯ ◯ X X

From the results shown in Table 3 and Table 4, the electrode11-electrode 13 of the examples 11-13, in which an area of no electrodeportion formed at vertically lower portion in respective cells was 18%,40%, 24% with respect to the projected area of respective cells, wereestimated as OK. However, the electrode 14 of the comparative examples11, in which an area of no electrode portion formed at vertically lowerportion in respective cells was 0% with respect to the projected area ofrespective cells, and the electrode 15 of the comparative example 12, inwhich an area of no electrode 10 portion formed at vertically upperportion in respective cells was 40% with respect to the projected areaof respective cells, were estimated as NG. Therefore, the followingswere understood.

-   (1) It is preferred that an area of no electrode portion formed at    vertically lower portion in respective cells is 5-50% with respect    to the projected area of respective cells.-   (2) It is further preferred that an area of no electrode portion    formed at vertically lower portion in respective cells is 15-50%    with respect to the projected area of respective cells.

Therefore, it is possible to obtain the image display panel having evenand excellent display function from the examples 11-13 corresponding tothe electrode 11-electrode 13, which satisfy all the conditions (1) and(2) mentioned above.

In the embodiment mentioned above, the electrodes (display electrode andopposed electrode are arranged to the substrates (transparent substrateand opposed substrate). In this case, a term “arranged to the substrate”means not only the case such that “the electrode is directly arranged onthe substrate” but also the case such that “the electrode is separatelyarranged on the substrate”.

Moreover, in the embodiments mentioned above, the explanation is made tothe particles, but, if substituting the particles for liquid powders,the present invention can be preferably applied as it is.

In the present invention, a term “liquid powder” means an intermediatematerial having both of liquid properties and particle properties andexhibiting a self-fluidity without utilizing gas force and liquid force.Preferably, it is a material having an excellent fluidity such thatthere is no repose angle defining a fluidity of powder. For example, aliquid crystal is defined as an intermediate phase between a liquid anda solid, and has a fluidity showing a liquid characteristic and ananisotropy (optical property) showing a solid characteristic (HeibonshaLtd.: encyclopedia). On the other hand, a definition of the particle isa material having a finite mass if it is vanishingly small and receivesan attraction of gravity (Maruzen Co., Ltd.: physics subject-book).Here, even in the particles, there are special states such as gas-solidfluidized body and liquid-solid fluidized body. If a gas is flown from abottom plate to the particles, an upper force is acted with respect tothe particles in response to a gas speed. In this case, the gas-solidfluidized body means a state that is easily fluidized when the upperforce is balanced with the gravity. In the same manner, the liquid-solidfluidized body means a state that is fluidized by a liquid. (HeibonshaLtd.: encyclopedia) In the present invention, it is found that theintermediate material having both of fluid properties and solidproperties and exhibiting a self-fluidity without utilizing gas forceand liquid force can be produced specifically, and this is defined asthe liquid powder.

That is, as is the same as the definition of the liquid crystal(intermediate phase between a liquid and a solid), the liquid powderaccording to the invention is a material showing the intermediate statehaving both of liquid properties and particle properties, which isextremely difficult to receive an influence of the gravity showing theparticle properties mentioned above and indicates a high fluidity. Sucha material can be obtained in an aerosol state i.e. in a dispersionsystem wherein a solid-like or a liquid-like material is floating in arelatively stable manner as a dispersant in a gas, and thus, in theimage display device according to the invention, a solid material isused as a dispersant.

When use is made of the liquid powders, in the image display deviceaccording to the invention, the liquid powders, which indicate a highfluidity in an aerosol state such that solid-like substances aresuspended in a gas stably as dispersoid, are sealed between opposed twosubstrates, at least one of two substrates being transparent. Suchliquid powders can be easily and stably moved by means of Coulomb'sforce and do on generating by applying a low voltage.

Then, the liquid powders will be explained.

As mentioned above, the liquid powders are an intermediate materialhaving both of liquid properties and particle properties and exhibitinga self-fluidity without-utilizing gas force and liquid force. The liquidpowders become particularly an aerosol state, and thus, in the imagedisplay device according to the invention, it is utilized under such acondition that a solid material is floated in a gas as a dispersant in arelatively stable manner.

As the aerosol state, it is preferred that an apparent volume in amaximum floating state is two times or more than that in none floatingstate, more preferably 2.5 times or more than that in none floatingstate, and most preferably three times or more than that in nonefloating state. In this case, an upper limit is not defined, but it ispreferred that an apparent volume is 12 times or smaller than that innone floating state.

If the apparent volume in the maximum floating state is smaller than twotimes, a display controlling becomes difficult. On the other hand, ifthe apparent volume in the maximum floating state is larger than 12times, a handling inconvenience during a liquid powder filling operationinto the device such as a particle over-scattering occurs. That is, itis measured by filling the liquid powders in a transparent closed vesselthrough which the liquid powders are seen; vibrating or dropping thevessel itself to obtain a maximum floating state; and measuring anapparent volume at that time from outside of the vessel. Specifically,the liquid powders having a volume ⅕ of the vessel are filled as theliquid powders in a vessel with a polypropylene cap having a diameter(inner diameter) of 6 cm and a height of 10 cm (product name I-boy®produced by As-one Co., Ltd.), the vessel is set in the vibrator, and avibration wherein a distance of 6 cm is repeated at a speed of 3reciprocating/sec. is performed for 3 hours. Then, the apparent volumein the maximum floating state is obtained from an apparent volume justafter a vibration stop.

Moreover, in the image display device according to the invention, it ispreferred that a time change of the apparent volume of the liquidpowders satisfies the floating formula:V₁₀/V₅>0.8;here, V₅ indicates the apparent volume (cm³) of the liquid powders after5 minutes from the maximum floating state; and V₁₀ indicates theapparent volume (cm³) of the liquid powders after 10 minutes from themaximum floating state. In this case, in the image display deviceaccording to the invention, it is preferred to set the time changeV₁₀/V₅ of the apparent volume of the liquid powders to larger than 0.85,more preferably larger than 0.9, most preferably larger than 0.95. Ifthe time change V₁₀/V₅ is not larger than 0.8, the liquid powders aresubstantially equal to normal particles, and thus it is not possible tomaintain a high speed response and durability according to theinvention.

Moreover, it is preferred that the average particle diameter d(0.5) ofthe particle materials constituting the liquid powders is 0.1-20 μm,more preferably 0.5-15 μm, most preferably 0.9-8 μm. If the averageparticle diameter d(0.5) is less than 0.1 μm, a display controllingbecomes difficult. On the other hand, if the average particle diameterd(0.5) is larger than 20 μm, a display is possible, but opacifying poweris decreased and thus a thin shape device is difficult. Here, theaverage particle diameter d(0.5) of the particle materials constitutingthe liquid powders is equal to d(0.5) in the following particle diameterdistribution Span.

It is preferred that particle diameter distribution Span of the particlematerials constituting the liquid powders, which is defined by thefollowing formula, is not more than 5 preferably not more than 3:Span=(d(0.9)−d(0.1))/d(0.5);here, d(0.5) means a value of the particle diameter expressed by μmwherein an amount of the particle materials constituting the liquidpowders having the particle diameter larger than this value is 50% andan amount of the particle materials constituting the liquid powdershaving the particle diameter expressed by μm wherein an amount of theparticle materials constituting the liquid powders having a particlediameter smaller than this value is 10%, and d(0.9) means a value of theparticle diameter expressed by μm wherein an amount of the particlematerials constituting the liquid powders having the particle diametersmaller than this value is 90%. If the particle diameter distributionSpan of the particle materials constituting the liquid powders is set tonot more than 5, the particle diameter becomes even and it is possibleto perform an even liquid powder movement.

Here, the particle diameter distribution and the particle diametermentioned above can be measured by means of a laserdiffraction/scattering method. When a laser light is incident upon theliquid powders to be measured, a light intensity distribution patterndue to a diffraction/scattering light occurs spatially. This lightintensity distribution pattern corresponds to the particle diameter, andthus it is possible to measure the particle diameter and the particlediameter distribution. In the present invention, it is defined that theparticle diameter and the particle diameter distribution are obtained bya volume standard distribution. Specifically, the particle diameter andthe particle diameter distribution can be measured by means of ameasuring apparatus Mastersizer 2000 (Malvern Instruments Ltd.) whereinthe liquid powders setting in a nitrogen gas flow are calculated by aninstalled analysis software (which is based on a volume standarddistribution due to Mie's theory).

The liquid powders may be formed by mixing necessary resin, chargecontrol agent, coloring agent, additive and so on and grinding them, or,by polymerizing from monomer, or, by coating a particle with resin,charge control agent, coloring agent, and additive and so on.Hereinafter, typical examples of resin, charge control agent, coloringagent, additive and so on constituting the liquid powders will beexplained.

Typical examples of the resin include urethane resin, acrylic resin,polyester resin, acryl urethane resin, silicone resin, nylon resin,epoxy resin, styrene resin, butyral resin, vinylidene chloride resin,melamine resin, phenolic resin, fluorocarbon polymers, and it ispossible to combine two or more resins. For the purpose of controllingthe attaching force with the substrate, acryl urethane resin, acrylurethane silicone resin, acryl urethane fluorocarbon polymers, urethaneresin, fluorocarbon polymers.

Examples of the electric charge control agent include, positive chargecontrol agent include the fourth grade ammonium salt compound, nigrosinedye, triphenylmethane compound, imidazole derivatives, and so on, andnegative charge control agent such as metal containing azo dye,salicylic acid metal complex, nitroimidazole derivative and so on.

As for a coloring agent, various kinds of basic or acidic dye may beemployable. Examples include Nigrosine, Methylene Blue, quinolineyellow, rose bengal and do on.

Examples of the inorganic additives include titanium oxide, Chinesewhite, zinc sulfide, antimonial oxide, calcium carbonate, zinc white,talc, silica, calcium silicate, alumina white, cadmium yellow, cadmiumred, cadmium orange, titanium yellow, iron blue, ultramarine blue,cobalt blue, cobalt green, cobalt violet, ferric oxide, carbon black,copper powder, aluminum powder and so on.

However, if the above materials are only mixed or coated with nocontrivance, the liquid powder exhibiting an aerosol state cannot beobtained. The regular method of forming the liquid powder exhibiting anaerosol state is not defined, but the following method is preferablyused.

At first, inorganic fine particles having an average particle size of20-100 nm preferably 20-80 nm are preferably fixed on a surface ofmaterials constituting the liquid powder. Moreover, it is preferred totreat the inorganic fine particles by a silicone oil. Here, as for theinorganic fine particles, use may be made of silicon dioxide (silica),zinc oxide, aluminum oxide, magnesium oxide, cerium oxide, ferric oxide,copper oxide and so on. In this case, a method of fixing the inorganicfine particles is important. For example, use may be made of hybridizer(Nara Machinery Industry Co., Ltd.) or mechano-fusion (Hosokawa MicronCo., Ltd.), and the liquid powders showing an aerosol state are formedunder a predetermined condition (for example processing time).

Here, in order to further improve a repeating durability, it iseffective to control a stability of the resin constituting the liquidpowders, especially, a water absorbing rate and a solvent insolublerate. It is preferred that the water absorbing rate of the resinconstituting the liquid powders sealed between the substrates is notmore than 3 wt % especially not more than 2 wt %. In this case, ameasurement of the water-absorbing rate is performed according toASTM-D570 and a measuring condition is 23° C. for 24 hours. As for thesolvent insoluble rate of the liquid powders, it is preferred that asolvent insoluble rate of the liquid powders, which is defined by thefollowing formula, is not less than 50% more preferably not less than70%:solvent insoluble rate (%)=(B/A)×100;(here, A is a weight of the liquid powder before being immersed into thesolvent and B is a weight of resin components after the liquid powdersare immersed into good solvent at 25° C. for 24 hours).

If the solvent insoluble rate is less than 50%, a bleed is generated ona surface of the particle materials constituting the liquid powders whenmaintaining for a long time. In this case, it affects an adhesion powerwith the liquid powders and prevents a movement of the liquid powders.Therefore, there is a case such that it affects a durability of theimage display. Here, as a solvent (good solvent) for measuring thesolvent insoluble rate, it is preferred to use fluoroplastic such asmethyl ethyl ketone and so on, polyamide resin such as methanol and soon, acrylic urethane resin such as methyl ethyl ketone, toluene and soon, melamine resin such as acetone, isopropanol and so on, siliconeresin such as toluene and so on.

As for a filling amount of the liquid powders, it is preferred tocontrol an occupied volume (volume occupied rate) of the liquid powdersto 5-70 vol %, more preferably 10-65 vol %, most preferably 10-55 vol %of a space between the opposed substrates. If the volume occupied rateof the liquid powders is less than 5 vol %, a clear image display is notperformed, and if it exceeds 70 vol %, the liquid powders becomedifficult to move. Here, a space volume means a volume capable offilling the liquid powders obtained by substituting an occupied portionof the partition wall 4 and a seal portion of the device from a spacebetween the opposed substrates 1 and 2.

A surface charge density of a particle substance constituting the liquidpowders can be measured as mentioned below. That is, according to ablow-off method, the liquid powders and carrier particles aresufficiently contacted and a saturated charge amount thereof ismeasured, so that a charge amount per a unit weight of the liquidpowders can be measured. Then, a particle diameter and a specificgravity of the particle substance constituting the liquid powders areseparately measured, and the surface charge density of the liquidpowders is calculated by using them.

<Blow-Off Measuring Theory and Method>

In the blow-off method, a mixture of the liquid powders and the carriersare placed into a cylindrical container with nets at both ends, andhigh-pressure gas is blown from the one end to separate the liquidpowders and the carriers, and then only the liquid powders are blown offfrom the mesh of the net. In this occasion, charge amount of reverseblown polarity remains on the carriers with the same charge amount ofthe liquid powders carried away out of the container. Then, all ofelectric flux by this electric charge are collected to Faraday cage, andare charged across a capacitor with this amount. Accordingly, the chargeamount of the liquid powders is determined as Q=CV (C: capacity, V:voltage across both ends of the capacitor) by measuring potential ofboth ends of the capacitor.

In the invention, as a blow-off powder charge amount measuringinstrument, TB-200 produced by Toshiba Chemical Co., Ltd. was used,F963-2535 available-from Powder TEC Co., Ltd. was employed as the samekind of carriers, and a specific gravity of the particle substanceconstituting the liquid powder was measured by a multi-volume densitymeter H1305 produced by Shimadzu Corporation. Then, the charge densityper unit surface area (unit: μC/m²) was calculated.

INDUSTRIALLY APPLICABILITY

In the image display device according to the invention, it is possibleto provide the image display device having rapid response rate due to adry type display, simple construction, inexpensive cost and excellentstability, by constructing a new image display device in which imagedisplay elements enabling to move the particles, to which electrostaticfield is directly applied, are arranged in a matrix manner.

Moreover, in the first aspect of the invention, since a coating area ofthe electrode provided on two substrates respectively is patternizedwith respect to a projected area of respective cells, the unevenparticle distribution to the partition walls and the particle drop atthe center portion of respective cells can be prevented, and thus it ispossible to provide the image display device which can display even andexcellent image.

Further, in the second aspect of the invention, since in the case ofarranging the image display panel vertically in a stationary manner, theelectrode is patternized in such a manner that no electrode portion isformed at a vertically lower portion in respective cells, the unevenparticle distribution to the partition walls and the particle drop atthe center portion of respective cells can be prevented, and thus it ispossible to provide the image display device which can display even andexcellent image.

1. An image display device which comprises an image display panel, inwhich two or more groups of particles having different colors anddifferent charge characteristics are sealed in a plurality of cellsformed by partition walls between two substrates, at least one of twosubstrates being transparent, and, in which the particles, to which anelectrostatic field produced by electrodes provided to both of thesubstrates is applied, are made to move so as to display an image,characterized in that a coating area of the electrode provided on twosubstrates respectively is patternized with respect to a projected areaof respective cells.
 2. The image display device according to claim 1,wherein at least one of the electrodes provided on the two substratesrespectively has a coating area in respective cells of 5-99% withrespect to a projected area of respective cells.
 3. The image displaydevice according to claim 1, wherein at least one of the electrodesprovided on the two substrates respectively has a coating area inrespective cells of 30-90% with respect to a projected area ofrespective cells.
 4. The image display device according to claim 2 or 3,wherein a contact dimension between at least one of the electrodesprovided on the two substrates respectively and the partition wall isless than 50% of an inner peripheral dimension of respective cells. 5.An image display device which comprises an image display panel, in whichtwo or more groups of particles having different colors and differentcharge characteristics are sealed in a plurality of cells formed bypartition walls between two substrates, at least one of two substratesbeing transparent, and, in which the particles, to which anelectrostatic field produced by electrodes provided to both of thesubstrates is applied, are made to move so as to display an image,characterized in that, in the case of arranging the image display panelvertically in a stationary manner, the electrode is patternized in sucha manner that no electrode portion is formed at a vertically lowerportion in respective cells.
 6. The image display device according toclaim 5, wherein an area of the no electrode portion formed at avertically lower portion in respective cells is 5-50% with respect to aprojected area of respective cells.
 7. The image display deviceaccording to claim 5, wherein an area of the no electrode portion formedat a vertically lower portion in respective cells is 15-45% with respectto a projected area of respective cells.